CXCR4 is a G-protein coupled receptor is activated by a sole physiological agonist, the chemokine CXCL12 and functions to cause the migration of cells to the appropriate anatomical location during embryonic development and in response to stress in adults. CXCR4 is also involved in growth and/or metastasis of a number of cancers, is a co-receptor for HIV-1, and mutant CXCR4 causes an immunosuppressive condition known as WHIM syndrome. A chemokine released by herpesvirus-8, v-MIP-II, is an antagonist of CXCR4. CXCL12 and vCCL2 belong to different subfamilies of the chemokine family as defined by their sequence and structure, and would be expected to expected to activate receptors within their subfamily. This proposal aims to determine the three-dimensional structures of the structures of CXCR4 complexed to (a) mutated CXCL12P2G that functions as an antagonist and (b) CXCL12P2G in the context of another mutation (H25R), which is predominantly a monomer in solution. Glycosaminoglycans are known to interact with most chemokines and promote the formation of dimers and oligomerization. Crystallization in the presence and absence of a heparin disaccharide known to bind CXCL12 at two locations (determined by X-ray crystallography in the PI's lab) and to promote dimerization will also be performed to test the hypothesis that glycosaminoglycans present chemokines to their receptors. These structures will be compared to each other and the CXCR4-AMD3100 (a small molecule antagonist) complex, a complex which has been crystallized by the collaborator (Dr. Ray Steven's, Scripps Institute) and its high resolution structure is in progress. Structural work with CXCR4 will lay the foundation for future work involving endogenous and HIV-1 proteins that bind CXCR4 and have medical relevance. PUBLIC HEALTH RELEVANCE: The chemokine receptor CXCR4 is a G-protein coupled receptor involved in HIV-1 entry, the metastasis and growth of several cancers and, when mutated at the C-terminus, responsible for the immunosuppressive disorder known as WHIM syndrome. It is also the target of the drug, Plexifor, for CD34+ peripheral cell mobilization used for multiple myeloma and non-Hodgkin's lymphoma. This proposal seeks to determine the three-dimensional structure of CXCL12 complexed to CXCR4.